Highly cut-resistant yarn and protective articles made therefrom

ABSTRACT

A cut-resistant composite yarn, comprising a high strength organic fiber having a tenacity greater than 15 grams per denier and a hard-particle-filled thermoplastic fiber useful in making fabrics from which protective articles, such as gloves are made.

This is a divisional application that claims priority from U.S. application Ser. No. 10/997,721, filed on Nov. 23, 2004.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates to cut-resistant fibers and yarns and particularly their use in gloves and other protective apparel.

2. Description of Related Art

Improved resistance to cutting with a sharp edge has long been sought. Cut-resistant gloves are beneficially utilized in the meatpacking industry and in automotive applications. As indicated by U.S. Pat. Nos. 4,004,295, 4,384,449, and 4,470,251, and by EP 458,343, gloves providing cut resistance have been made from yarn which includes flexible metal wire or which consist of highly oriented fibers having high modulus and high tensile strength, such as aramids, thermotropic liquid crystalline polymers, and extended chain polyethylene. A drawback to gloves made from yarn that includes flexible metal wire is hand fatigue with resultant decreased productivity and increased likelihood of injury. Moreover, with extended wear and flexing, the wire may fatigue and break, causing cuts and abrasions to the hands. In addition, the wire will act as a heat sink when a laundered glove is dried at elevated temperatures, which may reduce tensile strength of the yarn or fiber, thereby decreasing glove protection and glove life.

Improved flexibility and comfort and uncomplicated laundering are desirable in cut-resistant, protective apparel. Therefore, there is a need for a flexible, cut-resistant fiber that retains its properties when routinely laundered. Such a fiber may be advantageously used in making protective apparel, in particular highly flexible, cut-resistant gloves.

Polymers have been mixed with particulate matter and made into fibers, but not in a way that significantly improves the cut resistance of the fiber. For example, small amounts of particulate titanium dioxide have been used in polyester fiber as a delustrant. Also used in polyester fiber is a small amount of colloidal silicon dioxide, which is used to improve gloss. Magnetic materials have been incorporated into fibers to yield magnetic fibers. Examples include: cobalt/rare earth element intermetallics in thermoplastic fibers, as in published Japanese Patent Application No. 55/098909 (1980); cobalt/rare earth element intermetallics or strontium ferrite in core-sheath fibers, described in published Japanese Patent Application No. 3-130413 (1991); and magnetic materials in thermoplastic polymers, described in Polish Patent No. 251, 452 and also in K. Turek et al., J. Magn. Magn. Mater. (1990), 83 (1-3), pp. 279-280. Also, U.S. Pat. No. 5,597,649 is directed to a yarn, which is a composite of a high modulus fiber and a particle-filled fiber, wherein the high modulus fiber can be an aramid fiber.

Various kinds of gloves have been made in which metal has been included in the fabrication of the glove to impart protective qualities to the glove. For example, U.S. Pat. Nos. 2,328,105 and 3,185,751 teach that a flexible, X-ray shield glove may be made by treating sheets of a suitable porous material with a finely divided, heavy metal which may be lead, barium, bismuth or tungsten, or may be made from a latex or dispersion containing heavy metal particles. As illustrated by U.S. Pat. No. 5,020,161, gloves providing protection against corrosive liquids have been made with a metal film layer. These gloves also do not appear to have significantly improved cut resistance.

SUMMARY OF THE INVENTION

In one embodiment, this invention is a cut-resistant composite yarn, comprising a high strength organic fiber having a tenacity greater than 15 grams per denier and a hard-particle-filled thermoplastic fiber useful for making cut-resistant fabrics that can be made into protective articles, such as gloves, aprons, chaps, sleeves, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a and 1 b are schematic sketches of the chamber used in the Torture Chamber Test.

FIG. 2 is a sketch of a test glove as used in the Torture Chamber Test.

DETAILED DESCRIPTION OF THE INVENTION

The invention is a highly cut resistant yarn and articles for personal protective use such as gloves, aprons, chaps, and the like and the process for manufacturing them. The articles are made from yarns that are a combination of a high strength organic fiber and a thermoplastic carrier fiber filled with hard particles.

Within the embodiment of this invention the term “high strength organic fiber” is understood to mean a fiber with a tenacity greater than 15 grams per denier that is formed by any of the polymerization reactions commonly known in the art from monomers based on a carbon backbone. Preferably, high strength organic fibers do not include carbon fiber. Typical high strength organic fibers embodied by this invention include but are not limited to fibers with a tenacity greater than 15 grams per denier formed from para-aramid, polybenzazole, polybenzoxazole, polybenzothiazole, polybenzimidazole, polyacrylate, and copolymers thereof.

In one embodiment of this invention, the carrier fiber is formed from an isotropic semi-crystalline polymer. Typical fibers are fibers formed from polymers such as poly (alkylene terephthalate), poly (alkylene naphthalate), poly (arylene sulfide), aliphatic, and aliphatic-aromatic polyamide, and polyesters made from monomer units derived from cyclohexanedimethanol and terephthalic acid. In another embodiment of this invention, the carrier fiber is formed from a liquid crystalline polymer (LCP) that is preferably thermotropic. Typical LCP fibers are formed from polymers such as aromatic polyester, aliphatic-aromatic polyester, aromatic poly (estercarbonate), aliphatic-aromatic poly (esteramide), aromatic poly (esterimide), aromatic poly (esteramide), aromatic polyamide, aliphatic-aromatic polyamide, and poly (azomethine).

The hard particles used to fill the thermoplastic fibers of this invention may be characterized as having a MOHS hardness value of greater than 5. Preferably, the average particle size distribution of the hard particles will be in the range of 1 to 6 microns. Typical materials that may comprise the hard particles include but are not limited to tungsten, copper, brass, bronze, aluminum, steel, iron, monel, cobalt, titanium, magnesium, silver, molybdenum, tin, zinc, aluminum oxide, tungsten carbide, metal nitrides, metal sulfates, metal phosphates, metal borides, silicon dioxide, silicon carbide, baddelyte, chloritoid, clinozoiste, chondrodite, euclasite, petalite, sapphire, spodumene, staurolite, clay, or alumina.

In one embodiment of this invention, the hard particle filled thermoplastic fiber is a thermoplastic fiber in which the hard particle filler is essentially uniformly distributed. The hard particle filler is present in the amount of 0.1 to 10 (optionally 0.1 to 5) weight percent based on the total weight of the particle filled fiber.

In another embodiment of this invention, the hard particle filled thermoplastic fiber is the core fiber of a sheath/core fiber in which the hard particle filler is essentially uniformly distributed within the core material of the sheath/core fiber. Preferably, the hard particle filler is present in the amount of 0.1 to 10 (optionally 0.1 to 5) weight percent based on the total weight of the sheath/core fiber.

The articles are preferably made by knitting from yarns that are comprised of a combination of poly (paraphenylene terephthalamide) fiber sold by E.I. du Pont de Nemours and Company (DuPont), Wilmington, Del. under the trade name KEVLAR® and polyester CRF (cut resistant fibers). The polyester CRF is preferably an alumina-filled (about 10%) multifilament yarn as generally described in U.S. Pat. No. 5,851,668. The polyester is preferably poly (ethylene terephthalate). The polyester cut resistant fibers are available from Honeywell under the trademark Barricut®. The inventive yarns comprise about 32 to 65% of cut resistant polyester fiber; however, as the percentage cut resistant polyester increases beyond about 65%, the performance in cut protection decreases. The cut-resistant fabric that is a combination of KEVLAR® and polyester has cut resistance as measured by ASTM F1790-97 greater than that of a comparable weight fabric made entirely of either fiber. Additionally, unlike an article made wholly of polyester cut-resistant fabric, an article made of the inventive fabric is very resistant to cutting in shearing operations, such as with scissors.

Further, such articles in the form of gloves demonstrate exceptionally long life in the torture chamber test (TCT). The inventive gloves demonstrated dramatically better performance than gloves made either wholly of KEVLAR® or wholly of polyester CRF. Dupont developed the TCT (described in detail below) to evaluate the performance of cut resistant material in extreme conditions, where standard cut protection performance tests do not accurately predict performance in real-life situations.

The ply-twisted yarns of this invention are made by twisting together at least two individual single yarns. It is well known in the art to twist single yarns together to make ply-twisted yarns. Each single yarn can be, for example, a collection of staple fibers spun into what is known in the art as a spun staple yarn.

By the phrase “twisting together at least two individual single yarns”, it is meant the two single yarns are twisted together without one yarn fully covering the other. This distinguishes ply-twisted yarns from covered or wrapped yarns where a first single yarn is completely wrapped around a second single yarn so that the surface of the resulting ply-twisted yarn only exposes the first single yarn.

The ply-twisted yarns of this invention are preferably made up of at least two different single yarns. The ply-twisted yarns also preferably have a total linear density of from 300 to 2000 dtex. The individual fibers in a single yarn typically have a linear density of 0.5 to 7 dtex, with the preferred range being 1.5 to 3 dtex. The ply-twisted yarns, and the single yarns that make up those ply-twisted yarns, can include other materials as long as the function or performance of the yarn or fabric made from that yarn is not compromised for the desired use.

Test Methods

The cut protection Performance test (CPPT) was performed in accordance with ASTM F1790-97.

Tabor Abrasion Resistance was measured in accordance with ASTM D3389.

The scissor cut resistance test was performed by cutting the article with a pair of 8-inch carbon steel scissors of the type commonly used for household or office applications and subjectively evaluating the relative ease/difficulty encountered in cutting.

The torture chamber test is conducted in a 16-inch diameter Lucite cylinder 10 closed at both ends, which is depicted schematically in FIGS. 1 a and 1 b. Six (6) blade holders 12 are mounted on the inside of the cylinder around the periphery at 60 degree intervals (cylinder inside diameter is 14.5 inches). Each blade holder accepts 4 single edge razor blades 14 angled front-to-back in the cylinder at 45 degrees. Red Devil single edge industrial razor blades are used. The cylinder is rotated around its central axis, driven by an electric motor, not shown. The rotational speed of the cylinder was 35 revolutions per minute. The respective materials were tested in the form of gloves. Each glove was filled with 400 gm of nylon pellets and the glove was closed at the wrist to contain the pellets and then was placed alone in the Torture Chamber. The test glove is depicted schematically in FIG. 2. New razor blades were used for each glove evaluation. Time to failure was defined as the time when nylon pellets were first observed in the Torture Chamber. The test is discontinued if no pellets are observed within 180 minutes. Immediately upon observing any beads, rotation of the Torture Chamber was stopped and the glove was removed and examined for visual confirmation of a cut. This was to ensure that the glove had actually failed and that the pellets had not been released because the tied-off wrist area had loosened.

EXAMPLES

The materials were evaluated by knitting the various fibers into fabric samples or into gloves as required for the specific tests.

Example 1 and Comparative Examples A and B

Knitted fabric samples at 12.5 oz/yd² basis weight were made as follows: Comparative Example A 100% polyester CRF Comparative Example B 100% KEVLAR

Example 1

52% KEVLAR/48% CRF, wherein the KEVLAR and CRF were combined to produce co-twisted (plied) yarns. Two of the co-twisted yarns were then co-fed into the knitting machine to produce the fabrics.

The results of CPPT and Tabor Abrasion testing are provided in Table 1. TABLE 1 Example CPPT Tabor Abrasion Resistance A 1125 gms 325 cycles B  775 gms 360 cycles 1 1255 gms 430 cycles

Example 2-3 and Comparative Examples C and D

Knitted fabric and gloves at 19 oz/yd² basis weight were made as follows:

-   -   Comparative Example C 100% polyester CRF     -   Comparative Example D 100% KEVLAR

Example 2

68% KEVLAR/32% polyester CRF, wherein knitting was done utilizing three feed yarns, whereby two of the yarns were as described in Example 1 and the third feed yarn was 100% KEVLAR.

Example 3

35% KEVLAR/65% polyester CRF, wherein knitting was done utilizing three feed yarns, whereby two of the yarns were as described in Example 1 and the third feed yarn was 100% polyester CRF

The following test results provided in Table 2 are from fabrics, except for the torture chamber tests, which were performed on gloves made from the respective fabrics. TABLE 2 Torture Scissor Example CPPT Tabor Abrasion Chamber Life Resistance C 1525 gms 790 cycles 0.2 minutes easy D 1185 gms 440 cycles 15 minutes difficult 2 1750 gms 120 minutes difficult 3 2259 gms 90 minutes Not tested 

1. A protective article, comprising a fabric of cut-resistant composite yarn, comprising a high strength organic fiber having a tenacity greater than 15 grams per denier and a hard-particle-filled thermoplastic fiber, wherein the protective article is selected from the group consisting of aprons, chaps, sleeves and gloves.
 2. The article of claim 1, wherein the fabric is woven.
 3. The article of claim 1, wherein the fabric is knit.
 4. A glove in accordance with claim 1, wherein the torture chamber life of the glove exceeds the torture chamber life of a glove of equal basis weight consisting of only one fiber of the yarn.
 5. The glove of claim 4, having a torture chamber life of at least 90 minutes when the basis weight of the fabric is at least 19 oz/yd².
 6. A glove made from a cut resistant fabric, comprising a cut-resistant composite yarn, wherein the yarn comprises poly (paraphenylene terephthalamide) and poly (ethylene terephthalate) filled with about 0.1 to 10 weight percent of hard particles, based on the total weight of hard particles plus poly (ethylene terephthalate), having a torture chamber life of at least 90 minutes when the basis weight of the fabric is at least 19 oz/yd². 